DESCRIPTION: The goals of this project are to develop two explicit accounts of age effects in visual attention: 1) a model of complete RT distributions using a random walk model, and 2) a model of visual encoding functions. The experiments will involve making measurements of subjects' reaction times and accuracies under a variety of visual display conditions. Experiments 1-3 will use long-duration (unmasked) targets, and various display and stimulus variables will be manipulated. Random walks will be fitted to the complete RT distributions, and the best-fit parameters will yield information about age-group differences in attentional mechanisms. Experiments 4-6 will use short-duration (masked) targets, and accuracy will be measured as a function of target duration. These encoding functions are expected to allow age-group comparisons of attentional facilitation by taking sensory factors into explicit account. Experiments 7-8 will extend the current methods of analysis to a related attention paradigm. Analyses from the proposed project will allow us to understand better the mechanisms of age-related change in attentional facilitation.